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Measuring student growth: At a glance

In this era of No Child Left Behind, schools are receiving credit for students who achieve a state's "proficient" level, regardless of how far they progressed to get there. But, determining which students achieve more—high-scoring students who start out as a high-performers or average-scoring students who start at the bottom—is also important. Growth models can help schools and districts see just how much academic progress their students are making by measuring it between two points in time.

The terms "value added" and "growth models" are often the cited statistical methods for measuring student growth for accountability purposes. But what exactly are they? Do they measure what they claim? How should they be used? More important, as a school policymaker, educator, parent, or voter, why should you care?

Terms you should know

Status model: A method for measuring how students perform at one point in time. For example, the percent of fourth graders scoring at proficient or above in 2006.

Growth model: A method for measuring the amount of academic progress each student makes between two points in time. For example, Johnny showed a fifty point growth by improving his math score from three hundred last year in the fourth grade to three hundred fifty on this year's fifth grade exam.

Value-Added model: A method of measuring the degree in which teachers, schools, or education programs improve student performance.

Achievement level: Established categories of performance that describe how well students have mastered the knowledge and skills being assessed. For this guide, we use advanced, proficient, basic, and below basic for achievement levels. Proficient or above is assumed to represent the level that meets the state standard.

Scale score: A single numeric score that shows the overall performance on a standardized test. Typically, a raw score (number of questions answered correctly) is converted to a scale score according to the difficulty of the test and/or individual items. (For example, the 200–800 scale used for the SAT.)

Vertical scale scores: Numeric scores on standardized tests that have been constructed so that the scale used for scoring is the same for two or more grade levels. Hence, a student's scale score gain over multiple years represents the student's level of academic growth over that period of time.

  • Why are policymakers talking about growth models?
    Although schools are held accountable for student achievement, many educators and researchers believe that reporting student growth provides a more accurate picture of school effectiveness than the current snapshot of achievement because it does not take into account where a student started academically. But what makes sense in principle may have unintended implications depending on how growth models are used.

  • What are the different types of growth models? 
    The terms "growth model" and "Value-Added" are often used interchangeably. But Value-Added is only one of several types of models that measure student growth. It is also the only model designed to determine which aspect of schooling (e.g., school, teacher, education program) is responsible for a students' growth. In this section, we walk through the basic categories of growth models and discuss how each model works best.

    • Improvement Model
    • Performance Index Model
    • Simple Growth Model
    • Growth to Proficiency Model
    • Value-Added Model
  • What is needed to implement a growth model?
    As a system of measurement, there are certain features that should be in place in order to ensure that the growth model provides information that is reliable, valid, and useful, particularly if it is used for high-stakes accountability such as NCLB. These include:

    • Statement of policy intent: Being clear about how the information will be used.

    • Properly designed, annual tests: Making sure the instruments are appropriate for the purpose.

    • Data systems to collect, sort, and analyze the data: Having the technological capacity to track individual students' progress and other characteristics through the school system and match them with each school they attend.

    • Statistical Expertise: Hiring or assigning trained experts to oversee the design and implementation of the growth model.

    • Professional development: Targeting training to all stakeholders—teachers, principals, school board members, administrators, parents, and students—to help them understand exactly what is being measured and how to use the information effectively.

    • Transparency and good communication: Helping to assure non-statisticians (e.g., teachers, administrators) that the statistically complex growth model being used is valid by opening up the methodology to outside researchers for review.

    • Funding: Committing funds necessary to develop, implement, and maintain growth models, which are typically more expensive to administer than most current systems. Keep in mind that costs will vary depending on how many of the above elements may already be in place.

  • What are the limitations of growth models? 
    Growth models can be important tools for evaluating schools, teachers, and education programs, but like any measurement model they have their limitations. Anyone using growth information should be aware of these limitations to get the most from the data. For example:

    • Measures of achievement can be good, but none are perfect: Many of the tests administered by states are not designed for measuring growth, which can complicate using them for this purpose.

    • There is no data for untested subjects: In many states, measuring growth will be limited to reading and math (because typically other subjects are not tested).

    • There can be missing or incomplete student data: Students' high mobility at both the school and district level can affect the quality of information provided by some growth models.

    • Experts dispute how completely "Value-Added" growth models capture teacher, program, or school effectiveness: There is an ongoing debate among statisticians about the extent to which value-added models can isolate the effectiveness of a teacher, an education program, or a school on student learning. The risk of false conclusions can have serious implications, especially when using Value-Added measures for teacher evaluation.

    • A single growth model does not serve all purposes: It's important to design an appropriate model for your intended use.

    • Measuring growth in high schools is difficult: Most states either do not have annual tests in high school or they administer end-of-course tests that are not necessarily aligned to previous tests, something that is needed to measure growth.

  • How can growth models be used effectively?
    While growth models are not perfect, researchers believe they provide more accurate measures than most status models (e.g., student performance at one point in time) being used today (McCaffrey, Lockwood, Koretz, Louis, et al. 2004). By acknowledging their limitations and working to minimize them, growth models can be used effectively and provide valuable information that would not otherwise be available, including:

    • School accountability: The U.S. Department of Education reviewed over twenty state plans for implementing growth models as part of their accountability measures for NCLB and has approved nine. The approved plans incorporated targets for both growth and one hundred percent student proficiency by 2014 as required by law.

    • Teacher evaluation: While researchers emphasize that data about their students' growth should not be the only tool used to evaluate teachers, it is nonetheless a potentially valuable indicator to include among others.

    • Improving practice: Quite possibly the most effective use of information from growth models is not for high stakes accountability but for such low stakes applications as informing instructional improvement, evaluating the effectiveness of academic programs, and targeting professional development for teachers and administrators.

    • Teacher assignments: Administrators can also use growth data when assigning teachers in order to make the best match between teachers' strengths and students' needs.

    • Evaluating teacher preparation programs: Louisiana has taken the lead in using value-added models to connect student learning to graduates of its education schools as a means of evaluating the effectiveness of its university teacher preparation programs.

Growth models can be sophisticated tools that help gauge how much student learning is taking place. But like all tools, they are most effective in the hands of those who understand how to use them. This guide illustrates why.


The document was written by Jim Hull, policy analyst, Center for Public Education.Special thanks to Cyndie Schmeiser and Jeff Allen at ACT, Inc.; Mary Delagardelle and staff at the Iowa School Boards Foundation; and Joseph Montacalvo for their insightful feedback and suggestions. However, the opinions and any errors found within the paper are solely those of the author.

Posted: November 9, 2007

©2007 Center for Public Education